1. Field of the Invention
The present invention generally relates to a light source and, in particular, to a light emitting device.
2. Description of Related Art
Distinct from regular fluorescent lamps or incandescent lamps that generate heat to emit light, semiconductor light emitting devices such as light emitting diodes (LEDs) adopt the specific property of semiconductor to emit light, in which the light emitted by the semiconductor light emitting devices is referred to as cold luminescence. The light emitting devices have advantages of long lifetime, light weight, high brightness, and low power consumption, such that the light emitting devices have been employed in a wide variety of applications, such as optical displays, traffic lights, data storage apparatus, communication devices, illumination apparatus, medical treatment equipments, and 3C products. Accordingly, how to improve the light emitting efficiency of light emitting devices is an important issue in this art.
FIG. 1 is a schematic cross-sectional view of a conventional LED. Referring to FIG. 1, the LED 100 is a vertical type LED, which includes electrodes 110 and 120, and a light emitting layer 130. As shown in FIG. 1, the tight lines represent high current density, and the area with most number of lines is located between the electrodes 110 and 120. However, due to the congenital deficiency, the area with highest light emitting efficiency is blocked by the electrode 110, such that the overall light emitting efficiency of the LED 100 is adversely affected.
FIG. 2 is a schematic top view of another conventional LED. Referring to FIG. 2, the LED 200 is a horizontal type LED, which includes electrodes 210 and 220. Because the current always transmits through a path with lowest resistance, the distribution of the current density is inhomogeneous between the electrodes 210 and 220, where the main distribution of the current density is along the direct path between the electrodes 210 and 220. Therefore, in order to increase the amount of light emitted by the LED 200, the uniform current distribution area is needed to be enlarged, such that the size of the LED 200 is enlarged.
Based on aforesaid description, it is concluded that the light emitting efficiency of the LED may be influenced by the following factors.
1. The area between the electrodes of the LED is not only the area with highest current carrier density, but also the area producing most photons. However, the photons produced between the electrodes are mostly blocked by the opaque electrode, such that the light emitting efficiency is hard to be enhanced.
2. A current always transmits through a path with lowest resistance, which results in inhomogeneous luminance of the LED, such that the light emitting efficiency and the size of the LED are also limited.